Semiconductor light emitting elements, such as light emitting diodes, and semiconductor light receiving elements, such as photodiodes, are known as the semiconductor optical devices. Light emitting diode and photodiode are formed of semiconductor chips, each including an n-type region, a p-type region, and in many cases an active region disposed between the n-type and the p-type regions. In most cases, individual semiconductor chips (dies) are mounted in respective packages. Even in case of forming an optically active plane or surface, individual semiconductor chips serving as point elements are often located and distributed to form a plane. Description will be made hereinafter on semiconductor light emitting elements such as light emitting diodes, by way of example.
Light emitting diodes distributed in predetermined plane constitute assembly of point light sources. For example, traffic signal light in which a multiplicity of light emitting diodes are distributed in circular light emitting plane is used. An observer located near the traffic signal light can recognize that a multiplicity of light emitting diodes are disposed in a circular light emitting plane. It will be more preferable if the circular light emitting plane can uniformly emit light. In such use as illuminating a wide area uniformly, a plane-shaped light source is desirable. For example, in case of using a light emitting diode as backlight of a liquid crystal display, lights emitted from the light emitting diode may be introduced in diffusion plate having light scattering function, to constitute pseud-plane light source.
Light emitting diodes (LEDs) using nitride semiconductors such as GaN (gallium nitride) can emit ultraviolet light or blue light. By using fluorescence material, lights of three primary colors or white lights can be emitted. The light emitting diode has semiconductor lamination including, at least, an n-type semiconductor layer, an active layer for emitting light, and a p-type semiconductor layer. When nitride series semiconductor is used as the semiconductor lamination, for example a sapphire substrate is used as a growth substrate for growing the nitride series semiconductors. From the viewpoint of convenience of epitaxial growth, usually an n-type layer is first grown on a growth substrate, and an active layer and a p-type layer are grown thereon.
Sapphire substrate has low thermal conductivity, and hence is poor in heat dissipating ability. Sapphire substrate is therefore not fitted for such devices which are driven at large power, such as high power LED. In recent years, technology of laser lift-off is developed, in which on a sapphire substrate, nitride semiconductor lamination is grown, a p-side electrode is formed on the p-type layer, and a support substrate of silicon etc. having a high heat dissipating ability is bonded thereon, thereafter laser light is irradiated from the sapphire substrate side, to partially decompose the epitaxial layer, and to lift-off the sapphire growth substrate (for example, JPA 2006-128710). When a non-transparent support substrate such as silicon is used, output light cannot be derived through the support substrate. On the n-type semiconductor layer exposed by lifting-off the sapphire growth substrate, an n-side electrode can be formed. In this case, since current can be flown across the thickness direction of the semiconductor lamination, it is effective in reducing the resistance in the current path.
As p-type electrode, for example, a p-side transparent electrode and a reflecting electrode are formed over almost the whole area of the light emitting area of the p-type semiconductor layer. The efficiency of deriving lights can be improved by reflecting lights directed toward the support substrate. The n-side electrode is formed on at least part of the surface of the n-type semiconductor layer, which serves as light emitting surface. Lights emitted from the active layer, are partly emitted directly from the n-type semiconductor layer, and are partly transmitted through the p-side transparent electrode formed on the p-type semiconductor layer, then reflected by the reflecting electrode, and emitted through the n-type semiconductor layer.
The light emitting diode usually includes a growth substrate or a support substrate in part of the structure. When a light emitting diode having an area larger than a certain degree is to be constructed only with epitaxial layers, the strength usually becomes insufficient. When a growth substrate is to be removed, a support substrate is usually bonded.
There are proposals (for example, JPA 2011-77447) of designing bear chips of light emitting diodes smaller than the conventional typical minimum size (300 μm×300 μm), and handling only the epitaxial laminations. A plurality of single crystal semiconductor thin films are arranged in a predetermined plane, and the plane is constructed as assembly of light sources. For example, light emitting members having a size of 100 μm are disposed at a pitch of 200 μm, or light emitting members having a size of 10 μm are disposed at a pitch of 20 μm. The plane of the light emitting area is arranged to have a desired shape.
Respective light emitting members may be formed as follows. Semiconductor lamination is formed on a growth substrate through a sacrificial layer, and island-shaped trapezoidal patterns are shaped by mesa-etching. The sacrificial layer is selectively etched off to lift off the patterned semiconductor laminations from the growth substrate.